Template::TT3::Type::Params is a wafer thin subclass of
Template::TT3::Type::Hash
.
It is used to store named parameters that are passed to a subroutine or object method from TT.
The subroutine/method can inspect the final argument passed to see if it
is an instance of Template::TT3::Type::Params.
foo({ a = 10, b = 20 }) # regular hash array
foo(a = 10, b = 20) # named params